Structures in the inner ear that are concerned with the sensation of balance.

SEMILUNAR VALVES:

The heart valves that separate each ventricle from the great artery with which it is connected (either aorta or pulmonary artery). The semilunar valve on the right side of the heart is known as the pulmonic valve, and the corresponding valve on the left side is called the aortic valve.

SEMINAL VESICLES:

Pouches attached to the urinary bladder.

SEMINIFEROUS TUBULES:

Small channels within the testes wherein the spermatozoa (sperm) develop.

SEMINOMA:

The most common type of testicular tumor in the horse.

SEPTIC ARTHRITIS:

Inflammation of the joints caused by an infectious agent, usually bacterial.

SEPTIC SHOCK:

Shock caused by invasion of the body by bacteria that produce substances injurious to cells such that the cells can no longer utilize oxygen.

SEPTICEMIA:

The presence of bacteria in the blood circulation, accompanied by related clinical signs of disease.

SEPTUM (PLURAL: SEPTA):

A dividing wall, such as that dividing the right and left sides of the heart or the right and left nasal cavities.

SEQUESTRUM (PLURAL: SEQUESTRA):

A fragment of dead bone that has broken off from the underlying normal bone tissue.

SEROLOGY:

The use of specialized diagnostic tests for the detection of antigens and antibodies in serum.

SEROTYPE:

Variant of an infectious agent based on immunological testing.

SEROVAR:

Variant or subspecies of leptospire.

SERTOLI CELLS:

Cells within the testicular tubules that are important for nuture and development of spermatozoa (sperm).

SERUM:

Blood plasma minus the clotting factor fibrinogen; the clear liquid that remains after the blood clots, containing many important blood proteins including antibodies (immunoglobulins).

SERUM ALKALINE PHOSPHATASE (SAP):

An enzyme present in the blood that is produced in many body tissues and is of greatest diagnostic significance in diseases of the bone and liver.

SERUM HEPATITIS:

An acute form of liver failure in adult horses associated in most cases with the injection of some biological product of equine origin, usually tetanus antitoxin; also called Theiler's disease.

SESAMOID BONE:

Any small, nodular bone (such as the kneecap) that is located within the tendon of a muscle or the capsule of a joint.

Lethal, inherited disease of Arabian foals, characterized by an absence of T- and B-lymphocytes. Approximately 2% of Arabian foals are born with this condition.

SEX-LINKED DISEASES:

Genetic diseases of males caused by defective genes located on the X chromosome; also called X-linked diseases.

SEXUAL DIMORPHISM:

Size differences between the sexes, as seen with certain parasites.

SHAKER FOAL SYNDROME:

Form of botulism in 2- to 8-week-old foals that occurs following ingestion of Clostridium botulinum spores and their transformation into mature, toxin-producing bacterial forms in the intestinal tract.

SHAPING:

In training, the gradual refining or improvement of a task or movement.

SHEARED HEELS:

Breakdown of the tissue between the bulbs of the heel, caused by the hoof wall's being out of balance.

SHEATH:

Fold of skin enclosing the penis; prepuce.

SHOCK:

Failure of the blood vascular system to provide adequate circulation to the vital organs; circulatory collapse.

SHOE BOIL:

Common term for olecranon bursitis.

SIALOLITH:

Small stony concretion that forms within a duct draining a salivary gland, potentially resulting in blockage of the duct.

SIDEBONES:

Term describing ossification (bone formation) of the collateral cartilages of the foot; usually occurs in the forefeet of horses with poor conformation.

SIGN:

A characteristic of a disease; "signs" are seen by observation, while "symptoms" are characteristics reported by the patient; thus, animals exhibit signs of disease, while human beings report symptoms.

SINOATRIAL (SA) NODE:

A collection of specialized cardiac muscle fibers found at the junction of the right atrium and the vena cava; the heart's natural pacemaker, generating the electrical discharges that stimulate the beating and pumping of the heart.

SINUS EMPYEMA:

Formation of pus in the paranasal sinuses; the underlying cause in many cases is dental disease.

SINUSITIS:

Inflammation of a sinus.

SKELETAL MUSCLE:

The type of muscle making up most of the muscles of movement attached to the skeleton; also known as striated muscle.

SKEWBALD:

White and any color other than black (horse coloration).

SLEEPING SICKNESS:

Common term for the depression and somnolence characteristic of equine viral encephalomyelitis.

SMEGMA:

Thick, oily or cheesy secretion that collects beneath the sheath of the penis.

SMOOTH MOUTH:

"Smoothing" of the tooth surfaces seen in very old horses.

SMOOTH MUSCLE:

The type of muscle found in the walls of blood vessels and the major internal organs.

SOFT PALATE:

At the rear of the mouth, the soft, fleshy posterior partition separating the nasal and oral cavities.

SOFT-TISSUE ORBIT:

The nonbony structures (muscles, nerves, blood vessels) that lie within the bony orbit.

SOLUBLE FIBERS:

Dietary fibers as found in fruits, oat bran, and psyllium (the chief component of commercial stool softeners such as "Metamucil"); they attract water and form a gel, are highly fermentable (able to be digested by bacteria) in the large intestine, and have been shown in people to slow emptying of the stomach and to inhibit the absorption of cholesterol.

SOMATOMEDINS:

Small proteins produced mainly in the liver that exert an anabolic effect on the body, resulting in proliferation of bone, cartilage, and soft tissues, and enlargement of body organs; also known as insulinlike growth factors.

SOW MOUTH:

Dental malformation consisting of an underextended upper jaw.

SPASMODIC COLIC:

Colic characterized by increased numbers of bowel movements and episodes of pain following sudden changes in environmental temperature, diet, or activity level.

SPECIES:

One of the major classifying categories of taxonomy, representing divisions of a genus, and sometimes further classified into subspecies.

SPECIFIC GRAVITY:

A measurement of the concentration of urine in a urine sample; determined by using a small hand-held device called a refractomer.

SPERMATIC CORD:

Combined structure extending from the groin area to the testes, through which run the vas deferens and a number of vessels and nerves.

SPERMATOGENESIS:

The process whereby sperm cells within the testes of the stallion undergo cell divisions and cellular changes that result in the produce of mature spermatozoa (sperm).

SPERMATOZOA (SINGULAR: SPERMATOZOON):

The mature reproductive cells of the male; produced by the testes, their role is to fertilize the female egg (ovum).

SPHERULE:

The parasitic, noninfectious stage of the fungus Coccidioides immitis, formed during the organism's growth phase in host tissue.

SPHINCTER:

Circular band or ring of muscle that serves to open or close a tube or orifice; analogous to a valve.

SPINAL NERVES:

Nerves arising from the spinal cord that form nerves of the peripheral nervous system.

SPIROCHETES:

Filamentous, spiral-shaped bacteria, such as the leptospires and Borrelia.

SPLEEN:

Large abdominal organ that removes senescent (aged) red blood cells and foreign material from the bloodstream; an important component of the immune system.

SPLENECTOMY:

Surgical removal of the spleen.

SPLINT BONES:

The second and fourth metacarpal bones of the forefoot, attached to the cannon bone by interosseous ligaments.

SPLINTING:

Tightening of the muscles in an area in order to avoid pain associated with muscle movement.

SPLINTS:

Inflammation of the interosseous ligament that attaches the splint bones to the cannon bone.

SPORE:

Highly resistant, thick-walled "resting stage" formed by certain bacteria, to ensure their survival during periods of unfavorable environmental conditions; it germinates quickly once favorable conditions have been restored to produce a new generation of bacteria. Also, a general term referring to the reproductive cells of certain microorganisms, particularly fungi and protozoa.

SPOROCYST:

Larval stage of flukes that arises from the free-swimming miracidium stage.

In certain protozoa, the daughter cells resulting from division of a fertilized cell (zygote).

SPRAIN:

Joint injury involving damage to one or more ligaments, but without actual ligament rupture.

SQUAMOUS CELL CARCINOMA:

A malignant skin tumor of cells within the squamous cell layer of the epidermis.

SQUAMOUS CELL LAYER:

A layer of cells within the epidermis, the outermost layer of the skin; also known as the prickle cell layer, it lies above the basal cell layer and below the granular cell layer.

STALL-WALKING:

A stable vice characterized by constant circling, the horse's feet describing a roughly circular path through the bedding material on the floor of the stall.

STANDING HEAT:

Behavioral estrus; the full behavioral signs of estrus.

STENOSIS:

A constriction or narrowing of a vessel or duct.

STEP MOUTH:

Abnormality of older horses characterized by a wavelike or stair-step configuration of the premolars and molars from front to back; also called wave mouth.

STEREOPSIS:

Depth perception.

STERNAL:

Resting on the breastbone or sternum.

STERNUM:

Breastbone.

STEROID HORMONES:

Hormones manufactured by the body from cholesterol and protein.

STERTOR:

Noisy breathing.

STIFLE JOINT:

Joint where the femur joins the tibia; equivalent to the human knee joint.

STOMATITIS:

Inflammation of the lining of the mouth.

STRANGLES:

Extremely important, highly contagious bacterial disease of young horses caused by Streptococcus equi; characterized by inflammation of the pharyngeal mucous membranes, with swelling, inflammation, and abscess formation in the associated lymph nodes; also called distemper.

STRANGULATION:

Constriction resulting in impairment of the blood supply.

STREPTOTHRICOSIS:

Dermatophilosis.

STRIATED MUSCLE:

Skeletal muscle.

STRICTURE:

Narrowing of the diameter of a hollow tube, usually the result of contraction caused by local tissue damage.

STRIDOR:

Loud, strained, high-pitched noise on inhalation.

STRINGHALT:

Condition in which the horse involuntarily hyperflexes the hock as it walks; the cause is unknown.

STROBILA:

The body of a tapeworm parasite, comparised of a chain of segments called proglottids.

STRONGYLES:

Nematode parasites of horses; come in two varieties, large and small strongyles

SUBCUTANEOUS (SC):

Beneath the skin; a route of injection.

SUBCUTANEOUS EDEMA:

Accumulation of fluid beneath the skin.

SUBCUTIS:

The skin layer lying beneath the dermis, and composed of fat cells and strands of collagenous connective tissue; also called hypodermis.

SUBFERTILITY:

A state of being less than normally fertile, but not infertile.

SUBGINGIVAL:

Below the gumline.

SUBINVOLUTION:

Partial involution (return to normal size) of an organ, as of the uterus following delivery of the fetus.

SUBLUXATION:

Partial dislocation of a joint; also, a slight alteration in the position of the lens of the eye.

SUBMANDIBULAR:

Beneath the lower jaw.

SUCROSE:

Table sugar.

SULFUR GRANULES:

Yellowish clumps of bacteria mixed with dead and dying cells, commonly observed in the pus draining from lesions of actinomycosis.

SUMMER SORES:

Common term for cutaneous habronemiasis.

SUPPURATIVE:

Producing pus (said of bacterial infections).

SURFACTANT:

A soaplike substance produced by specialized cells lining the alveoli of the lungs; responsible for decreasing the pressure (surface tension) within the alveoli and preventing them from collapsing during normal respiratory movements.

SUTURE:

A surgical stitch.

SWAMP FEVER:

Equine infectious anemia.

SWEENY:

Atrophy of the supraspinatus and infraspinatus muscles, located over the scapula (shoulder-blade); usually caused by damage to the nerve supply to these muscles.

SWEET ITCH:

Queensland itch.

SYMPTOMATIC THERAPY:

Therapy aimed at alleviating the signs or symptoms of a disease rather than treating its underlying cause.

SYNAPTIC CLEFT:

The space between an axon terminal and the myofiber it supplies, and across which the nerve impulse is transmitted by means of "messenger molecules" such as acetylcholine.

SYNGAMY:

Alternative term for gametogamy.

SYNOVIAL FLUID:

Joint fluid, the material that lubricates the joint surfaces.

SYNOVIAL MEMBRANE:

The lining membrane of a joint.

SYNOVITIS:

Inflammation of the lining membrane of a joint.

SYSTEMIC:

Throughout the body; pertaining to the body as a whole.

SYSTEMIC LUPUS ERYTHEMATOSUS (SLE):

A rare, chronic, multisystemic autoimmune disorder, characterized by the production of autoantibodies to DNA and normal cellular constituents.

SYSTOLE:

The contraction/ejection phase of the heartbeat.

SYSTOLIC BLOOD PRESSURE:

The pressure that occurs when the heart contracts and pushes blood into the arterial system.